Australia's incoming deluge: 'Strong odds' of significantly wetter than usual weather in the NT, Queensland as Pacific Ocean gives clues that La Nina could return

Sky News AU

13 hours ago

There are strong odds of Australia's late winter and spring months being wetter than usual - and significantly so in the NT and Queensland - with Pacific Ocean indicators pointing to a potential La Nina event in 2025.
The year so far has been marked by rain and floods in the east and drought in the south, with wet weather now suddenly picking up in the drought-stricken southern growing regions that need it most.
Now, this Sky News Weather climate analysis can reveal that many more rain-bearing systems are on the way. Indian Ocean
Avid weather watchers will no doubt be aware that there is plenty of talk about a negative phase of the Indian Ocean Dipole (-IOD) developing and aiding rainfall across Australia.
The Indian Ocean lies to Australia's west.
It is currently in a neutral state with the IOD sitting at -0.04C.
This value needs to fall below -0.4C for at least eight consecutive weeks for these developments to be declared a -IOD event.
It's still a long way off, but forecast models have been in strong agreement for some time that an event is a significant chance to take place.
Its influence could be noticeable from as early as late August if it drops below the threshold in the coming weeks. Pacific Ocean
The ocean to our east is the largest in the world – covering more than 30 per cent of the world's surface.
Its size and proximity have contributed to its outsized influence on our weather.
This mass expanse of water has played a significant role in helping the last five financial years exceed the nation's median rainfall.
We had three back-to-back La Ninas, then an El Nino then a 'La Nina-like' pattern that was declared by Sky News Weather and US Government's climate organisation NOAA, but not by the Bureau of Meteorology.
Right now, the official value of the Nino3.4 index is –0.14C.
However, when comparing the temperatures in the middle of the Pacific Ocean to those through the rest of the world's tropics we can see that we are more clearly on the La Nina side of neutral.
The Relative NINO index is therefore more appropriate to use in a changing climate – currently sitting closer to –0.4C.
Forecast models have suddenly come into line agreeing that significant cooling of the central Pacific is likely.
Between July and September, the median of nine leading models cools the NINO region by between 0.2C and 0.7C with an average of 0.45C.
Therefore, there is a significant chance that the September value of the Relative NINO index will be close to -0.8C.
This puts us on the border of a weak La Nina event.
But like last year, even if it cools a bit further than that, the Bureau will probably say we are experiencing 'La Nina-like conditions' without declaring an event - as official thresholds are unlikely to be met. Rain odds increasing for most
According to the average of the nine aforementioned models – including the Bureau's – there is between a 60 per cent and 90 per cent chance of above median rainfall across Australia from August to October.
This is a notable increase on the previous forecast for the same period – indicating the growing confidence in the upcoming rainfall pattern.
The odds are strongest in the NT and Queensland – meaning that parts of the dry season and 'build-up' months could be significantly wetter than usual – but this is still nothing compared to the wet season.
Further south, rainfall should also be very handy in drought affected regions of SA, Victoria and possibly Tasmania and Western Australia – although their rain chances are not quite as high.
Many farmers will remember the last time we had strong rain odds at this time of year.
Rain gradually picked up through the winter of 2022 before the country saw its second wettest spring on record.
Forbes experienced near-record flooding and the Murray had its biggest flood since 1956.
Models are not quite as extreme in their forecasts this year as they were in the lead up to that event.
However, similar rainfall patterns cannot be ruled out through the coming months as evidenced by this week's uptick in wet weather. Sydney and the NSW coastline could miss out
Sydney and the NSW coast have been pretty wet this year.
Historically the first half of the year is the wetter time of year in these areas.
It's therefore unlikely that the second half of the year will be wetter than the first half.
Further to that – a lot of the upcoming rainfall is expected to favour the NSW ranges and areas further west.
Therefore, it seems likely that rainfall in Sydney and up and down the NSW coast should be somewhat closer to normal.
Locals in those areas may not notice the drenching affecting much of the country.
Watch Sky News Weather on the Sky News App or on Foxtel's Channel 601 for the latest forecasts and seasonal outlooks.